Puff adders (Bitis arietans), like many other snakes, hiss as part of their defensive repertoire.

In B. arietans, the hisses have a clear quadraphasic pattern consisting of an initial exhalatory hiss, a brief transitional pause, an inhalatory
hiss and a rest or breath-holding phase. Simultaneous recordings of body diameter, electrical activity in the intrinsic laryngeal musculature,
airflow through the nasal passageway and sound production revealed that the anterior respiratory tract plays a passive role in hissing and that
the costal pump is responsible for generating the quadraphasic pattern. During hissing, B.arietans uses the same mechanics previously described
for normal respiratory ventilation in snakes.

Analyses of artificial hisses reveal that the anterior respiratory tract of B. arietans has little ability to modify an exhalant airstream acoustically.
The combination of the simple ventilatory mechanics used during hissing and the lack of acoustic modification of the exhalant airstream results in the
production of an acoustically simple hiss.

Cross-correlation matrix analyses of a variety of snake hisses showed a high degree of acoustic similarity between the sounds, almost approaching
the levels determined for white noise. This high level of acoustic similarity reflects the low level of acoustic specialization within the sounds produced
by snakes and the low potential for encoded information content.

Content from a very interesting paper about the mechanics of sound Production in Bitis aritans:
BRUCE A. YOUNG, NANCY NEJMAN, KAREN MELTZER AND JESSICA MARVIN
Department of Biology, Lafayette College, Easton, PA 18042, USA

the full article can be found:

here